1. Field of the Invention
The present invention relates to a current range control circuit, a data driver, and an organic light emitting display, and more particularly to, a current range control circuit, a data driver, and an organic light emitting display capable of controlling the range of the output currents of the data driver.
2. Discussion of Related Art
Recently, various flat panel displays of lower weight and volume than the traditional cathode ray tubes (CRT) have been developed. Flat panel displays include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the flat panel displays, the organic light emitting displays are spontaneous emission devices that emit light by re-combination of electrons and holes. The organic light emitting display may be referred to as an organic electroluminescent display. Compared to a passive electroluminescent device that requires an additional light source, such as an LCD, the organic light emitting display has high response speed more similar to the CRT.
The organic light emitting display may be driven either by a passive matrix method or an active matrix method. In the passive matrix method, an anode and a cathode are formed to intersect and a line is selected to be driven. In the active matrix method, the amount of current that flows through an electroluminescent device is controlled by an active device. A thin film transistor (TFT) is mainly used as the active device. The active matrix method is complicated, while having the advantages of low power consumption and long emission time.
The programming methods of the organic light emitting display are divided into a voltage programming method and a current programming method. In the voltage programming method, a data driver outputs a voltage corresponding to a data signal, a capacitor that is part of a pixel stores voltage corresponding to the output voltage, and an electroluminescent device emits light in response to the stored voltage. In the voltage programming method, it is possible to use the data driver used for the LCD as is. However, it is difficult to obtain a uniform image due to variation between the threshold voltage and mobility of the various TFTs used as the active device of the pixel circuit.
In the current programming method, the data driver outputs currents corresponding to the data signals, the capacitor built in the pixel stores the voltage corresponding to the output current, and the electroluminescent device emits light in response to the stored voltage. In the current programming method, it is possible to easily compensate for the variation of the threshold voltage and mobility of the TFTs and to thus obtain a uniform screen.
On the other hand, in the data driver of the current programming method, the range of the data currents may vary with the pixel circuit. In the case of the pixel circuit that transmits current whose magnitude is equal to the magnitude of the data currents, the required range of the data currents is not large. However, when the data currents are M times the current that flows through the electroluminescent device by using an M:1 current mirror, the range of the data currents is large. Also, because luminous efficiency varies with the type of the electroluminescent device, the required range of the data currents may vary. As described above, because the required range of the data currents varies with the type of the pixel circuit or the type of the electroluminescent device, a different data driver must be designed whenever the pixel circuit or the electroluminescent device change.